1. Field of the Invention
The invention relates to methods and apparatus for flexibly generating fine mists of liquids such as chemical solutions over a wide range of operating parameters, and to methods and apparatus for forming high quality thin films of various complex chemical compounds in a practical and efficient manner using mists of solutions containing the chemical compounds. More particularly, the invention relates to non-reactive, liquid source chemical vapor deposition (LSCVD) methods and apparatus for depositing high quality, stoichiometrically-correct, thin films of a large variety of complex chemical compounds in a practical and efficient manner utilizing mists of stable chemical solutions.
2. Description of Relevant Art
As discussed in the Background section of parent application Ser. No. 660,428, there are known methods and apparatus for depositing thin films of complex chemical compounds such as metal oxides, ferroelectrics, super-conductors, materials with high dielectric constants, gems, etc., although such known methods and apparatus have significant disadvantages associated therewith which prevent them from being adopted for manufacturing thin films of the chemical compounds on a practical, large scale.
In parent application Ser. No. 660,428, applicant has previously proposed novel methods and apparatus involving non-reactive LSCVD techniques which overcome the many problems and disadvantages associated with known deposition techniques for depositing thin films of complex chemical compounds and which can be used for easily and economically producing the thin films.
FIGS. 1-6 of the present application are duplicated from the Ser. No. 660,428 application and are representative of the methods and apparatus disclosed in the parent application.
Although applicant's previously proposed methods and apparatus function very effectively, applicant has found that such methods and apparatus remain to be improved, especially in relation to flexibility in processing parameters for depositing thin films of various chemical compounds.
Particularly, although applicant's previously proposed methods and apparatus can be used to efficiently deposit high quality thin films of many different chemical compounds on a practical, large scale, it is necessary to tune the deposition apparatus (especially the mist generators thereof, such as the one shown in FIG. 4) for each specific chemical which is to be deposited in relation to many processing parameters including temperature, viscosity of the chemical solution, vacuum level, volume of mist to be generated, etc. Once the proper combination of parameters is established for a given chemical compound, the previously proposed methods and apparatus function excellently to deposit high quality thin films of the compound, but the different operating parameters required for depositing different chemical compounds makes if difficult to quickly and efficiently utilize the previous methods/apparatus to deposit thin films of different compounds in succession.
The present invention has been developed to overcome the above disadvantages associated with applicant's previously proposed methods/apparatus, and to generally fulfilled a great need in the art by providing methods and apparatus for quickly, flexibly and efficiently depositing high quality thin film of different complex compounds in succession.
Additionally, according to applicant's previously proposed methods/apparatus different embodiments were disclosed in which thin films of chemical compounds are deposited using mists of solutions containing the compounds either by depositing thin films of the mists at ambient temperatures and subsequently drying same (as disclosed in relation to present FIGS. 1 and 6) or by dissociating the chemical compounds from the mists at elevated temperatures using various heating means in combination (one of which is a UV, spectral heat bath) such that the chemical compound deposits directly on a substrate (as disclosed in relation to present FIG. 5).
Applicant has discovered that a modification or hybrid of such previously disclosed methods works exceptionally well in obtaining high quality thin films of many complex compounds such a ferroelectrics. The modification involves implementation of a UV curing step between the drying step P.sub.11 and the high temperature annealing step P.sub.12 used according to the previously disclosed method shown in FIG. 6. More particularly, applicant has found that after a thin film of a solution is deposited from a mist at ambient temperature and subsequently dried according to the previously disclosed method, but before the thin film is high temperature annealed, if the dried film is cured under a UV spectral bath, the desirable dielectric characteristics of the film are tremendously improved.
The UV curing step is preferably carried out at relatively low temperatures of 100.degree.-350.degree. C., which are much less than the temperatures of 600.degree.-850.degree. C. typically required for the high temperature annealing of step P.sub.12. The UV curing is effectively a "cold annealing" step which functions to create better thin films of chemical compounds by breaking residual solvent bonds remaining in the dried films, thereby inducing additional, desirable crosslinking between molecules of the desired chemical compound in the film. For example, excess hydroxyl groups (OH) typically remain in a dried film according to applicant's previously disclosed methods/apparatus when the solvent of the chemical solution used is an alcohol. When excess hydroxyl groups in the thin film are broken, the resulting oxygen radicals link with other atoms in the film, thus enhancing the oxygen content in the thin film and creating better/stronger linking within the film.